Technical Discussion: Resolution & Image Brightness

I disagree that ISO affects how many photons are captured. ISO is just a gain setting and has nothing to do with how many photons are captured at the sensor.

"How is it that can I achieve the same brightness with different fluxes?"

AJSJones wrote in post #17452776
By changing the shutterspeed or aperture - those will affect how many of the photons in the incoming flux from the object will be captured or by changing the ISO, which alters how many captured photons will be set to 100% "brightness".

kb9tdj wrote in post #17452781
I disagree that ISO affects how many photons are captured. ISO is just a gain setting and has nothing to do with how many photons are captured at the sensor.

As I said, aperture and shutter affect how many are captured. How many get set to "100% brightness" is determined by the ISO/gain setting, no?

melcat wrote in post #17450391
No. The ADC is measuring the voltage output from the amplifier (whose gain is set by the ISO setting), and the maximum voltage of that amplifier is whatever the camera designer felt like making it. (For example, this is probably higher on a Canon camera than a Sony camera, because Sony do everything on the sensor chip but Canon run that voltage signal along a circuit board and they will want it to be robust against noise.)

An ADC requires a reference voltage which corresponds to all 1s on its output. That voltage will be higher if the maximum output voltage from a pixel after amplification is higher. Whether it's higher because the camera has fewer pixels or because of the camera design doesn't matter.

If the amplifier and ADC parameters are being altered to give equivolent brightness values in the RAW data, wouldn't that suggest that for sensors of increasing pixel density but the same well capacity, cameras need to come with lower and lower ISO gains? This way I can increase the output from the amplifier and into the ADC by capturing more photons in each pixel, rather than increasing the gain of the amplifier (and improve SNR I would think). Otherwise my saturation limit in the RAW data is going to be reached by the parameters on the amplifier and ADC working on the signal, rather than reaching well capacity in the pixels on the sensor when collecting photons.

Poe wrote in post #17452814
If the amplifier and ADC parameters are being altered to give equivolent brightness values in the RAW data, wouldn't that suggest that for sensors of increasing pixel density but the same well capacity, cameras need to come with lower and lower ISO gains? This way I can increase the output from the amplifier and into the ADC by capturing more photons in each pixel, rather than increasing the gain of the amplifier (and improve SNR I would think). Otherwise my saturation limit in the RAW data is going to be reached by the parameters on the amplifier and ADC working on the signal, rather than reaching well capacity in the pixels on the sensor when collecting photons.

When sensels are made smaller, they (generally) will collect fewer photons before they overflow (saturate) - that is the same as saying the "full well capacity" is decreased as sensels get smaller. If manufacturers could increase the well capacity dramatically without increasing the area, that would be an improvement (and we could have lower base ISO) - but I don't think that's what you refer to.

When the amplifier and ADC parameters are altered, that results in different incoming fluxes being assigned the same "100% brightness" IN THE FILE, NOT in the incoming image.

In one image, the brightest pixel in the file (256,256,256, in 8 bit RGB, for example) may have come from a flux of 10,000 photons/square micron/second, while in another file (with a different ISO, higher gain) that value will be given to a flux of only 1,000 photons/sq micron/second. The images will have the same max brightness on screen/print, but they came from very different scene brightnesses.

AJSJones wrote in post #17452837
When sensels are made smaller, they (generally) will collect fewer photons before they overflow (saturate) - that is the same as saying the "full well capacity" is decreased as sensels get smaller. If manufacturers could increase the well capacity dramatically without increasing the area, that would be an improvement (and we could have lower base ISO) - but I don't think that's what you refer to.

In some past discussion, I've encountered a statement that the photosite of the pixels have maintained the same area but manufacturers have reduced the non-photoactive area in order to increase pixel density (I didn't bookmark this so I can't reference it). So this would suggest that well capacity would stay the same up to the point that the area of the photosite had to be altered to continue increasing pixel density. I don't know if we're at the point or not but if there are discussions on this, I'd be interested to take a look.

The scenario that I put forward in my OP assumes the pixels have the same photosite and well capacity, just that the non-photoactive area has been altered to increase pixel density. It doesn't consider the situation where well capacity is increased by some means other than size of the photosite.

I'm afraid you are going to have to re-state your question, if you still have one - you've lost me. Roger Clark has some dicsussion of where technology has reached with regard to fill factor (photosentive area as a fraction of total sensel area) if that's where you are headed...

Poe wrote in post #17452871
In some past discussion, I've encountered a statement that the photosite of the pixels have maintained the same area but manufacturers have reduced the non-photoactive area in order to increase pixel density (I didn't bookmark this so I can't reference it). So this would suggest that well capacity would stay the same up to the point that the area of the photosite had to be altered to continue increasing pixel density. I don't know if we're at the point or not but if there are discussions on this, I'd be interested to take a look.

The scenario that I put forward in my OP assumes the pixels have the same photosite and well capacity, just that the non-photoactive area has been altered to increase pixel density. It doesn't consider the situation where well capacity is increased by some means other than size of the photosite.

If I understand what you're trying to say, it sounds like you're talking about the introduction of gapless micro-lenses.

Right. Or at least the assumption that the micro-lenses can focus all of the entering lightrays onto the photosite.